I know you could change the font/ text size by editing the font.ini file found in ressystem. That said, I never got it to work myself, I don't know if it still works, and I think it only applies to the chat or some other specific things. I've just seen screenshots a long time ago where people have used this. Maybe someone else here knows more.
Here's an old thread on FiestaFan that talks a little, tiny bit about it: http://www.fiestafan.com/forums/showthread.php?t=902 .
Aside from that I'm not aware of any way to change the text size beyond resolution.
Just to note: I suppose it would be considered file editing which might be against the ToS, but it's harmless on the same level as editing the UI - which is allowed. I guess a GM can just remove my post if this is unacceptable.